IJRET

1. IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
Volume: 03 Special Issue: 13 | ICNTCC-2014 | Sep-2014, Available @ http://www.ijret.org 209
EVALUATION OF POZZOLANIC REACTIVITY OF CALCINED
KAOLINITE
C. M. G. de Souza1
, S. Greiser2
, E. Garcia3
, V. A. Quarcioni4
, Ch. Jäger5
1,3,4
IPT-Institute for Technological Research, Brazil
2,5
BAM - Federal Institute for Materials Research and Testing, Germany
cmgsouza@ipt.br, edugarcia@ipt.br
Abstract
The need to improve the sustainability and the need for innovation in the cement industry has brought to light the practice of using
additives to the cement in order to decrease CO2 emissions in industrial plants and increase the quality of cement in terms of durability
and performance. Currently some additives have been employed as granulated blast furnace slag, limestone and pozzolan. The
additives give mortar and concrete larger energy efficiency, gain in durability and resistance, contributing to buildings with slender
structures and cheaper and durable maintenance. Besides natural pozzolan can be used artificial ones, as calcined clays, and over a
range of amorphous aluminates and silicates waste, with highly reactive function as a binder material in the presence of water and
calcium hydroxide. Calcined kaolinite clays were characterized using various techniques such as XRD, thermal analysis, and NMR
observing 27
Al and 29
Si nuclei. The results showed that there is a structural modification of the samples, from crystalline to amorphous
phases with the increasing of temperature in the calcination process. There is an improving in the reactivity of calcined clays by the
range of 600ºC to 750ºC temperature in the reaction with calcium oxide, according to data from Chapelle test, indicating the possibility
of using them as additives for cement and confirming their pozzolanic potential.
Keywords: kaolin, pozzolan, calcined clays, cement additive
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1. INTRODUCTION
The current Portland cement industry is undergoing major
changes. The questioning of their contribution to climate
change and the environment has led to increasing demand for
environmentally friendly and economical alternative for its
production, using a based on three basic pillars: greater energy
efficiency, additions to cement and alternative fuels. Also
notable is the need to make the final product, where the mortar
and concrete, more durable and more resistant, contributing to
buildings with slender structures and cheaper maintenance and
durable.
In Brazil for decades the cement industry has been using partial
additions replacement for Portland cement. This can be
considered a way to reduce their environmental liabilities. The
additives can be found of several types available in the
Brazilian market: CPII - E cement with the addition of
granulated blast furnace slag; CPII - F that receives the
addition of limestone filler; CPII-Z which receives the addition
of pozzolan [1]; CPIII with higher addition of granulated blast
furnace slag [2]; and CPIV with higher addition of pozzolan
[3]. The CPII-Z cement uses partial adding 6%-14% of
pozzolan material and CPIV uses 15%-50%, both replacing
clinker. These calcined particulate materials, added in part to
the clinker substitution, have predominantly amorphous
microstructure [1], [2].
Besides natural pozzolana one can use artificial pozzolans, as
calcined clays. Brazil is rich in kaolinite clays that can be used
as pozzolans after calcination at the appropriate temperature
[4], [5].
Pozzolanic chemical reactivity can be evaluated by Chapelle
test [6], [7]. The NBR 15.985 standard [6], published in Brazil
and the technique NF P18513 [7] published in French at same
time follow, the general guidelines described by Raverdy et al.
[8] with the basic difference that these two normative texts use
pozzolan: calcium oxide (CaO) 1:2 ratio to perform the test and
expresses the results in mg of calcium hydroxide (Ca(OH)2)
fixed per gram of the sample.
In this work calcined kaolinite clays were characterized by
various techniques such as X-ray diffraction (XRD), thermal
analysis, magic angle spinning nuclear magnetic resonance
(MAS-NMR), Blaine technique, BET analysis, for observing
structural changes during the calcination process, correlated to
formation of their meta-stable forms, improving the assessment
of kaolinite clays and its reactive potential. Data were also
studied and correlation between structural changes and
pozzolanic reaction were compared using dedicated
characterization techniques as MAS-NMR and Chapelle test.
The results showed that there is a structural modification of the
samples with the calcination process of the kaolinite clay.
There is an increasing from crystalline to amorphous phases,
with the increasing in the temperature of calcination. Data
compared between metakaolinite formation correlate to
pozzolanic reaction showed a changing in the reactivity to a
maximum at 700ºC calcined sample and the possibility of
using them as addictive to cement.

2. IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
Volume: 03 Special Issue: 13 | ICNTCC-2014 | Sep-2014, Available @ http://www.ijret.org 210
2. MATERIALS AND METHODS
Pozzolan material were obtained from sedimentary origin
kaolinite clay with chemical composition determined by
classical chemical analysis as follow: 51.77% SiO2, 29.45%
Al2O3; 2.22% Fe2O3; 2.87% K2O; 1.38% TiO2; Fire Loss
10.58% and other lesser extent. The material preparation
occurred by manual grinding with a mortar until fully passing
through sieve # 200mesh (65μm). The sample was calcined at
various temperatures from 500°C, 550°C, 600°C, 650°C,
700°C, 750°C, 800°C and 850°C after two hours without
heating ramp in a muffle furnace the material was cooled by
forced ventilation to gain amorphousness.
X-ray diffraction was performed a Rigaku Windmax 1000
equipment, with 2° ramp, 1° slit. An acceleration voltage of
40 kV and a current of 20 mA were applied. The thermal
analysis (TG / DTG / DTA) were performed using TA
Instruments SDT 2960 equipment in an open alumina crucible,
with Nitrogen 100mL/min purge, at a heating rate of 10°C/min.
The 27
Al magic angle spinning (MAS) NMR spectra were
obtained at the frequency of 156,38 MHz (14,1 Tesla) on a
BRUKER Avance 600 spectrometer using 2.5mm probe with
25kHz spinning speed rotation, 5.5 µs 90° pulse, and 2 s
repetition time. 29
Si MAS NMR spectra were obtained at the
frequency of 79.49 MHz (9.4 Tesla) on a BRUKER 400 DSX
spectrometer using 7mm probe with 6.5kHz spinning speed
rotation, 3.1 µs 90° pulse, and 5-120 s repetition time. Blaine
permeability was measured according to Brazilian standard
NBR NM67 [10] and laser BET granulometric analysis [11]
were performed on a Gemini V2.00 Micrometrics equipment
on nitrogen atmosphere with 3s equilibration time and 711.945
mmHg sat. pressure. The pozzolanic reactivity analysis was
performed with lime reaction according to the Chapelle test
using 1:2 pozzolan-CaO ratio in 16 hours test at 90° C (± 5),
with the result expressed as milligrams per gram of CaO fixed
material.
3. RESULTS AND DISCUSSIONS
3.1 XRD Characterization
Figure 1 illustrates the XRD pattern of kaolinite and calcined
kaolinite clays in different temperatures. The samples contain
both crystalline (kaolinite, muscovite and quartz plus traces of
potassium feldspar). The broad hump between 20 and 30° (at
2 values) indicates the presence of amorphous phases which
increases with increasing calcination temperature, to a
maximum at 700°C calcined sample.
Fig. 1 - Overlapping diffraction patterns of fresh (IN) and raw
material in various calcination temperatures. Highlight of
major peaks: Mu = Muscovite, Ka = kaolinite and Q = quartz.
3.2 DTA Characterization
The DTA curves shown in Figure 2 shows an endothermic
peak near 520ºC, due to the dehydroxylation of kaolinite in the
natural sample and confirmed the presence of mineral
compounds in the material [4], [9]. By 6.9% calculated
hydroxyl group losses can be inferred that the kaolinite
corresponds to approximately 50% in the sample. The
dehydroxylation peak was also observed sample calcined at
500ºC. TG data showed that the material gain mass stability
from 700°C calcined sample.
Fig. 2 - Differential thermal analysis curves at different
temperatures of calcination.

3. IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
Volume: 03 Special Issue: 13 | ICNTCC-2014 | Sep-2014, Available @ http://www.ijret.org 211
3.3 Blaine, BET characterization
The particles of the kaolinite clay in nature, manually
grounded, are largely formed by spheroids with small
dimensions and high specific surface area of 19.530 cm²/g as
measured by Blaine method and the value of 166.200cm²/g
analyzed by BET as showed in Table 1. Both techniques
showed that sample calcined at 550°C has a significant loss of
surface area by agglomeration of particles. When analyzed by
Blaine technique, sample calcined at 600°C showed the
tendency of particles to stabilize in spheroid shape, however,
the BET technique showed that these particles undergo
changes in its internal structure by opening the layers and
leaving more exposed surface for reactivity. It is important to
observe that temperatures above 600°C are related to the early
loss of oxygen bridges and disruption of the alumina layer by
changing the coordination of aluminum.
At 650°C the specific surface area returns to the value of
162.000cm² indicating a reorganization of the internal structure
of the particle which makes the area similar to that material
calcined at 550°C. The tendency of gradual increase in specific
surface area from temperature between 650°C and 750°C
analyzed by the BET technique showed area gain by increasing
the amount of amorphous keeping the size and shape of
spheroid particles.
At 750°C calcination temperature the BET determination of
surface area was slightly larger and the one measured by
Blaine was slightly smaller than the calcination at 700°C,
resulting in more particles agglutinated, and more amorphous.
Considering the results obtained from the two techniques, they
indicate a reduction of surface area from clay calcined at
800°C, both the external and internal area of the spheroids
sample.
Table 1 – Specific surface area of the samples.
Sample Blaine Technique BET Technique
in nature 19,550 166,200
550°C 17,701 161,100
600°C 17,160 175,000
650°C 17,020 161,800
700°C 17,170 165,200
750°C 16,850 171,100
800°C 16,360 170,700
3.4 Nuclear Magnetic Resonance
The 29
Si MAS-NMR spectra of kaolinite clay calcined in
different temperatures are shown in Figure 3. Spectra showed a
peak shift from 90ppm to 105ppm with the increasing of
calcination temperature, which could be related to structural
changes from high crystalline to high amorphous phases by
increasing the number of Q4(3Al) structure to Q4(1Al) and
Q4(4Si). Sample calcined at 500ºC showed a peak at -91.5ppm
due to kaolinite structure still present in the sample. This signal
has less intensity from sample calcined 550ºC. Sample calcined
at 800ºC and 850ºC showed peaks at -100ppm and -105ppm
due probably to the formation of Q4(1Al) e Q4(0Al)(4Si)
structure in the samples.
Fig. 3 - Evolution of the 29
Si MAS-NMR spectra in calcined
samples at different temperatures.
Observing the 27
Al MAS NMR spectra showed in Figure 4 it
can be observed a significant change in coordination of the
Aluminum sites in the samples, according to the increasing of
calcinations temperature. The sample calcined at 500ºC
presents a sharp peak at approximately 0ppm, referred to the
kaolinite phase still present in the clay. This peak is
characteristic of octahedral Al (Al(VI)). When the kaolinite is
calcined to higher temperatures the intensity of this peak
decreases and two lines in approximately 30 and 60ppm
increases indicating respectively an increase in aluminum-V
(Al(V)) and aluminum-IV (Al(IV)) sites. Calcined samples at
700°C and 750°C showed the highest Al(V) peaks (slightly
higher at 700° C) over Al(IV) and Al(VI).
Fig. 4 – Evolution of the 27
Al MAS-NMR spectra of calcined
samples in different temperatures.

4. IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
Volume: 03 Special Issue: 13 | ICNTCC-2014 | Sep-2014, Available @ http://www.ijret.org 212
The evolution of the transformation observed in the 27
Al and
29
Si MAS-NMR spectra suggests that silicates are freed from
their connections sheet of alumina with increasing temperature
to a maximum of 700°C, when it begins larger change in
chemical shift in 29
Si spectra and a small decrease in the
proportion Al(V), corresponding to structural modification of
metakaolin back to promote higher condensed silicate network
with less aluminum contained links between aluminates and
silicates.
3.5 Chapelle test
The results of the tests performed with standard NBR 15895
[6] in the calcined samples showed a level of reactivity
between 650°C and 750°C, with a tendency to peak at 700°C,
as shown in Figure 5. It is possible to observe that there is a
smooth trend pointing to 700°Cin the assay, like more reactive
material.
Fig. 5 - Results of the Chapelle test performed as Raverdy et al.
[8] and NBR 15 985 [6].
In a preliminary study Sanz et al. [12] raised a suspicion of
correspondence between reactivity observed and Al(V) sites in
the samples. With the quantification of this Al(V) by
integrating the peak areas it was observed that this species has
a significant evolution from the calcination at 600°C and
increases up to 43.7% of the total aluminum in the sample
when calcination is carried out at 700°C, with a lightly
decreasing for 750°C calcined sample. The sample to 800°C
temperature suggests that this modification of the structure of
the sheet silicates more sharply diminished reactivity of the
change in the coordination of the aluminum
Figure 6 showed a direct and proportional correlation between
the amounts of aluminum V obtained by 27
Al MAS-NMR
spectra with pozzolanic reactivity of metakaolin obtained by
Chapelle tests for each calcined sample. It was observed that
the evolution calcination temperature of the kaolinite sample
correspond to a proportionally larger amount of the reactive
aluminum V sites. These data indicate a high correlation
between the NMR techniques with Chapelle test.
Fig. 6 – Correlation between pozzolanic reaction observed by
Chapelle test and percentage of Al(V) obtained by 27
Al MAS-
NMR experiment.
CONCLUSIONS
All correlated techniques showed that there is a level of
pozzolanic reactions between the samples calcined at
temperatures between 600°C and 750°C with a higher
reactivity closely related to the specific area measured by
Blaine method. In this range of temperature of calcination there
is smaller coalescence of material as showed by Blaine specific
area. The evolution in the calcination temperature produces
larger particles, mainly in the range above 45μm, as
characterized by laser particle size. The changes highlighted by
technique BET / Blaine collaborate to better understand the
behavior of particles, not only with respect to their specific
area, but also with respect to the same format throughout the
various calcination temperatures.
The pozzolanic reactivity measured by Chapelle test using
pozzolan: CaO 1:2 ratio as described by the current NBR
15.985 was more appropriate than the 1:1 ratio originally
proposed by Raverdy et al in 1980, and actual Chapelle tests
showed the presence of a level of reactivity between the
samples calcined at temperatures between 650°C and 750°C
with the tendency of higher reactivity at 700°C.
29
Si and 27
Al MAS-NMR techniques of the calcined samples
showed that there is a structural modification of the samples,
from crystalline to amorphous phases with the increasing of
temperature in the calcination process. Which means a change
in silicon and aluminum coordination sites and this is related to
the reactivity of the samples, as compared with Chapelle tests.
The higher amount of Al(V) showed a higher reactivity of the
calcined samples, with the release of the silicates sheet for
reactivity.

5. IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
Volume: 03 Special Issue: 13 | ICNTCC-2014 | Sep-2014, Available @ http://www.ijret.org 213
REFERENCES
[1] ABNT – NBR 11,578 – Cement Compound Portland:
specification, Rio de Janeiro, Brazil, 1996.
[2] ABNT – NBR 5735 - Portland Cement Blast Furnace, Rio
de Janeiro, Brazil, 1991.
[3] ABNT - NBR 5736 - Pozzolanic Cement Porland, Rio de
Janeiro, Brazil, 1991.
[4] V. S. Ramachandran et al., Handbook of Thermal Analysis
of Construction Materials. Ottawa: ed. Willian Andrew
Publishing, New York Institute for Research in Construction,
National Research Council of Canada, 2002.
[5] Pérsio de Souza Santos, Ciência e Tecnologia das Argilas.
ed. Edgard Blücher, Universidade de São Paulo, São Paulo,
Brazil, vol. 1,2 and 3, 1989.
[6] ABNT – NBR 15,895 – Pozzolanic Materials -
Determination of calcium hydroxide content fixed - Chapelle
method, Rio de Janeiro, Brazil, 2012.
[7] AFNOR – NF P18,513 – Métakaolin, Addition Puozolani-
que pour Betons – Définition, Specifications, Crìteres de
Conformité, 2010.
[8] W. Raverdy et al., Appréciation de látivité puozolanique
des Constituants Secundaries, In: congress International de la
Chimie des Ciments, Paris, vol. III and IV, 1980.
[9] W. Smykatz-kloss. Differential Thermal Analysis:
Application and Results in Mineralogy, New York, ed.
Springer-Velag, 1974.
[10] ABNT – NBR NM67 - Determination of fineness by air
permeability method (Blaine method), Rio de Janeiro, Brazil,
1998.
[11] BET - Brunauer, Emmett and Teller test, Adsorption of
Gases in Multimolecular Layers, 1938.
[12] J. Sanz et al., Aluminum-27 and Silicon-29 Magic-Angle
Spinning Nuclear Magnetic Resonance Study of the Kaolinite-
Mullite Transformation, Journal of the American Ceramic
Society, vol. 71, C418-C421, 1988.
BIOGRAPHIES:
Claudia Maria G. de Souza has received her PhD. from
University of São Paulo, São Paulo, Brazil. Currently working
as researcher in the Chemical Analysis Lab. at IPT - Institute
for Technological Research. Her research interests are in the
field of nuclear magnetic resonance applied to material
characterization.
Eduardo Garcia has received the Msc. degree from the IPT-
Institute for Technological Research, São Paulo, Brazil.
Currently he is working as Professor in the department of Civil
Engineering at Universidade Paulista, and researcher at IPT.
His research interests include alkaline activation clays and
alternative materials for cement addition like pozzolans.
Sebastian Greiser has received his Graduate degree from
Leipzig University, Leipzig, Germany. Currently he is PhD
student at the BAM- Federal Institute for Materials Research
and Testing, Berlin, Germany. His research interests are in the
field of geopolymers.
Valdecir Angelo Quarcioni has his DSc. from University of
São Paulo, São Paulo, Brazil. Currently working as head of
Construction Materials Laboratory of IPT-Institute for
Technological Research. His interests are chemistry of building
materials, with emphasis on binders, waste materials, addition
for Portland cements and durability of mortar and concrete.
Christian Jäger has received his Ph.D. from the University of
Jena, Germany. Currently working as head of the NMR group
at the BAM- Federal Institute for Materials Research and
Testing, Berlin, Germany. His research interests are in the field
of nuclear magnetic resonance applied to material
characterization.